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Date: Thu, 1 Oct 2020 13:38:58 -0700 From: "Chang S. Bae" <chang.seok.bae@...el.com> To: tglx@...utronix.de, mingo@...nel.org, bp@...e.de, luto@...nel.org, x86@...nel.org Cc: len.brown@...el.com, dave.hansen@...el.com, jing2.liu@...el.com, ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org, chang.seok.bae@...el.com Subject: [RFC PATCH 07/22] x86/fpu/xstate: Introduce helpers to manage an xstate area dynamically task->fpu has a buffer to keep the extended register states, but it is not expandable at runtime. Introduce runtime methods and new fpu struct fields to support the expansion. fpu->state_mask indicates the saved states per task and fpu->state_ptr points the dynamically allocated area. alloc_xstate_area() uses vmalloc() for its scalability. However, set a threshold (64KB) to watch out a potential need for an alternative mechanism. Also, introduce a new helper -- get_xstate_size() to calculate the area size. No functional change until the kernel supports dynamic user states. Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com> Reviewed-by: Len Brown <len.brown@...el.com> Cc: x86@...nel.org Cc: linux-kernel@...r.kernel.org --- arch/x86/include/asm/fpu/types.h | 29 +++++-- arch/x86/include/asm/fpu/xstate.h | 3 + arch/x86/kernel/fpu/core.c | 3 + arch/x86/kernel/fpu/xstate.c | 124 ++++++++++++++++++++++++++++++ 4 files changed, 154 insertions(+), 5 deletions(-) diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index c87364ea6446..4b7756644824 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -327,14 +327,33 @@ struct fpu { */ unsigned long avx512_timestamp; + /* + * @state_mask: + * + * The state component bitmap. It indicates the saved xstate in + * either @state or @state_ptr. The map value starts to be aligned + * with @state and then with @state_ptr once it is in use. + */ + u64 state_mask; + + /* + * @state_ptr: + * + * Copy of all extended register states, in a dynamically-allocated + * area, we save and restore over context switches. When a task is + * using extended features, the register state is always the most + * current. This state copy is more recent than @state. If the task + * context-switches away, they get saved here, representing the xstate. + */ + union fpregs_state *state_ptr; + /* * @state: * - * In-memory copy of all FPU registers that we save/restore - * over context switches. If the task is using the FPU then - * the registers in the FPU are more recent than this state - * copy. If the task context-switches away then they get - * saved here and represent the FPU state. + * Copy of some extended register state that we save and restore + * over context switches. If a task uses a dynamically-allocated + * area, @state_ptr, then it has a more recent state copy than this. + * This copy follows the same attributes as described for @state_ptr. */ union fpregs_state state; /* diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 9aad91c0725b..37728bfcb71e 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -103,6 +103,9 @@ extern void __init update_regset_xstate_info(unsigned int size, u64 xstate_mask); void *get_xsave_addr(struct fpu *fpu, int xfeature_nr); +int alloc_xstate_area(struct fpu *fpu, u64 mask, unsigned int *alloc_size); +void free_xstate_area(struct fpu *fpu); + const void *get_xsave_field_ptr(int xfeature_nr); int using_compacted_format(void); int xfeature_size(int xfeature_nr); diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 875620fdfe61..e25f7866800e 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -235,6 +235,9 @@ int fpu__copy(struct task_struct *dst, struct task_struct *src) */ memset(&dst_fpu->state.xsave, 0, fpu_kernel_xstate_default_size); + dst_fpu->state_mask = xfeatures_mask_all & ~xfeatures_mask_user_dynamic; + dst_fpu->state_ptr = NULL; + /* * If the FPU registers are not current just memcpy() the state. * Otherwise save current FPU registers directly into the child's FPU diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 6e0d8a9699ed..af60332aafef 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -10,6 +10,7 @@ #include <linux/pkeys.h> #include <linux/seq_file.h> #include <linux/proc_fs.h> +#include <linux/vmalloc.h> #include <asm/fpu/api.h> #include <asm/fpu/internal.h> @@ -69,6 +70,7 @@ static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_comp_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; static unsigned int xstate_supervisor_only_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1}; +static bool xstate_aligns[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = false}; /* * The XSAVE area of kernel can be in standard or compacted format; @@ -128,6 +130,48 @@ static bool xfeature_is_supervisor(int xfeature_nr) return ecx & 1; } +/* + * Available once those arrays for the offset, size, and alignment info are set up, + * by setup_xstate_features(). + */ +static unsigned int get_xstate_size(u64 mask) +{ + unsigned int size; + u64 xmask; + int i, nr; + + if (!mask) + return 0; + else if (mask == (xfeatures_mask_all & ~xfeatures_mask_user_dynamic)) + return fpu_kernel_xstate_default_size; + else if (mask == xfeatures_mask_all) + return fpu_kernel_xstate_max_size; + + nr = fls64(mask) - 1; + + if (!using_compacted_format()) + return xstate_offsets[nr] + xstate_sizes[nr]; + + xmask = BIT_ULL(nr + 1) - 1; + + if (mask == (xmask & xfeatures_mask_all)) + return xstate_comp_offsets[nr] + xstate_sizes[nr]; + + /* + * Calculate the size by summing up each state together, since no known + * size found with the xstate area format out of the given mask. + */ + for (size = FXSAVE_SIZE + XSAVE_HDR_SIZE, i = FIRST_EXTENDED_XFEATURE; i <= nr; i++) { + if (!(mask & BIT_ULL(i))) + continue; + + if (xstate_aligns[i]) + size = ALIGN(size, 64); + size += xstate_sizes[i]; + } + return size; +} + /* * When executing XSAVEOPT (or other optimized XSAVE instructions), if * a processor implementation detects that an FPU state component is still @@ -268,10 +312,12 @@ static void __init setup_xstate_features(void) xstate_offsets[XFEATURE_FP] = 0; xstate_sizes[XFEATURE_FP] = offsetof(struct fxregs_state, xmm_space); + xstate_aligns[XFEATURE_FP] = true; xstate_offsets[XFEATURE_SSE] = xstate_sizes[XFEATURE_FP]; xstate_sizes[XFEATURE_SSE] = sizeof_field(struct fxregs_state, xmm_space); + xstate_aligns[XFEATURE_SSE] = true; for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { if (!xfeature_enabled(i)) @@ -289,6 +335,7 @@ static void __init setup_xstate_features(void) continue; xstate_offsets[i] = ebx; + xstate_aligns[i] = (ecx & 2) ? true : false; /* * In our xstate size checks, we assume that the highest-numbered @@ -753,6 +800,9 @@ static bool is_supported_xstate_size(unsigned int test_xstate_size) return false; } +/* The watched threshold size of dynamically allocated xstate area */ +#define XSTATE_AREA_MAX_BYTES (64 * 1024) + static int __init init_xstate_size(void) { /* Recompute the context size for enabled features: */ @@ -777,6 +827,14 @@ static int __init init_xstate_size(void) if (!is_supported_xstate_size(fpu_kernel_xstate_default_size)) return -EINVAL; + /* + * When observing the allocation goes beyond the threshold, it is better to consider + * switching a better scalable mechanism than the current. + */ + if (fpu_kernel_xstate_max_size > XSTATE_AREA_MAX_BYTES) + pr_warn("x86/fpu: xstate buffer too large (%u > %u)\n", + fpu_kernel_xstate_max_size, XSTATE_AREA_MAX_BYTES); + /* * User space is always in standard format. */ @@ -867,6 +925,12 @@ void __init fpu__init_system_xstate(void) if (err) goto out_disable; + /* + * At this point, it passed the size sanity check. Have the init_task take + * the feature mask. + */ + current->thread.fpu.state_mask = (xfeatures_mask_all & ~xfeatures_mask_user_dynamic); + /* * Update info used for ptrace frames; use standard-format size and no * supervisor xstates: @@ -1086,6 +1150,66 @@ static inline bool xfeatures_mxcsr_quirk(u64 xfeatures) return true; } +void free_xstate_area(struct fpu *fpu) +{ + vfree(fpu->state_ptr); +} + +/* + * Allocate a new xstate area with a calculated size, based on the given bit value. + * + * No mechanism implemented yet to shrink or reclaim the xstate area on the fly, + * the need of which is subject to the real usage. + */ +int alloc_xstate_area(struct fpu *fpu, u64 mask, unsigned int *alloc_size) +{ + union fpregs_state *state_ptr; + unsigned int oldsz, newsz; + u64 state_mask; + + state_mask = fpu->state_mask | mask; + + oldsz = get_xstate_size(fpu->state_mask); + newsz = get_xstate_size(state_mask); + + if (oldsz >= newsz) + return 0; + + if (newsz > fpu_kernel_xstate_max_size) { + pr_warn_once("x86/fpu: state buffer too large (%u > %u bytes)\n", + newsz, fpu_kernel_xstate_max_size); + XSTATE_WARN_ON(1); + return 0; + } + + /* + * The caller may be under interrupt disabled condition. Ensure interrupt + * allowance before the memory allocation, which may involve with page faults. + */ + local_irq_enable(); + /* We need 64B aligned pointer, but vmalloc() returns a page-aligned address */ + state_ptr = vmalloc(newsz); + local_irq_disable(); + if (!state_ptr) + return -ENOMEM; + + memset(state_ptr, 0, newsz); + if (using_compacted_format()) + fpstate_init_xstate(&state_ptr->xsave, state_mask); + + /* + * As long as the register state is intact, save the xstate in the new area at + * the next context copy/switch or potentially ptrace-driven xstate writing + */ + + vfree(fpu->state_ptr); + fpu->state_ptr = state_ptr; + fpu->state_mask = state_mask; + if (alloc_size) + *alloc_size = newsz; + return 0; +} + static void fill_gap(struct membuf *to, unsigned *last, unsigned offset) { if (*last >= offset) -- 2.17.1
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